1. Field of the Invention
This invention relates to a refrigerator used in a biochemical analysis apparatus which is capable of accommodating a film feed cassette in such a way that the cassette can be released therefrom. The film feed cassette houses a long test film which has not yet been used in an analysis of a liquid sample. This invention also relates to a dry air generating device which continuously generates dry air and which is suitable for use with the refrigerator, and a method for operating the dry air generating device.
2. Description of the Prior Art
Qualitative or quantitative analyses of specific chemical constituents in liquid samples are conducted for various industrial purposes. Particularly, it is very important in biochemical and clinical fields to be able to quantitatively analyze certain chemical or physical constituents in body fluids, such as blood or urine.
Recently, as disclosed in, for example, Japanese Patent Publication No. 53(1978)-21677 and Japanese Unexamined Patent Publication No. 55(1980)-164356, a dry type chemical analysis slide was developed for use in a system designed for performing quantitative analyses, with which system the amount of a specific chemical constituent or a specific physical constituent contained in a droplet of a liquid sample, which is applied to the slide, is determined. It is possible to analyze a liquid sample more simply and more quickly with methods in which a chemical analysis slide is used than with methods in which a conventional wet type analysis is carried out. Therefore, it is more desirable to use chemical analysis slides, particularly in medical organizations, research laboratories, or the like, where many samples must be analyzed, than to carry out conventional wet type analyses.
In order to use a chemical analysis slide in the analysis of a chemical constituent or the like contained in a liquid sample, a measured amount of the liquid sample is put on the chemical analysis slide and is kept at a predetermined temperature (i.e. incubated) for a predetermined time in an incubator, which causes a color reaction. The chemical analysis slide is then exposed to light having a wavelength which is selected in advance, the selection of which wavelength depends on the constituents of the liquid sample and the constituents of a reagent contained in the reagent layer in the chemical analysis slide. Light is thus irradiated to a reaction product which forms on the chemical analysis slide, and the ratio of transmitted vs. reflected light is found. Thereby quantitative analysis of a chemical constituent or the like in a sample is carried out.
In medical organizations, research laboratories or the like, where many liquid samples are analyzed, it is desirable to conduct analyses automatically and sequentially. To satisfy this need, various chemical analysis apparatuses have been proposed, which use the aforesaid chemical analysis slides. One such chemical analysis apparatus is disclosed in, for example, Japanese Unexamined Patent Publication No. 56(1981)-77746. Also, as a means with which liquid samples can be automatically and sequentially analyzed, an apparatus is proposed in, for example, U.S. Pat. No. 3,526,480, in which apparatus a long tape-like test film containing a reagent is used instead of the aforesaid chemical analysis slides, and the application, incubation and measurement of samples are carried out sequentially on adjacent portions of the test film. The operating cost of an apparatus using a long tape-like test film is lower than the operating cost of an apparatus using chemical analysis slides, and a simple mechanism makes it possible for measurements to be carried out sequentially on many liquid samples.
The long test film may be housed in a film feed cassette by being wound around a feed reel and then loaded into the biochemical analysis apparatus. The film feed cassette is provided with a film outlet. The long test film is affected by temperature or humidity and will deteriorate (i.e. the chemical properties of the long test film will change) if the temperature and humidity are not closely controlled. In order to eliminate this problem, the biochemical analysis apparatus may be provided with a refrigerator which is kept at a low temperature and low humidity. A long test film is housed in the film feed cassette and then accommodated in the refrigerator so that it does not deteriorate even if a long time occurs between when it is loaded into the apparatus and when analysis begins. Also, the film feed cassette contains a desiccant, and the space inside the film feed cassette is kept in a dry state (at humidity of 0%) before the film feed cassette is loaded into the refrigerator. The refrigerator is provided with a cassette accommodating section which is enclosed by a refrigerator wall and in which the film feed cassette is accommodated releasably. Additionally, the refrigerator has a film outlet at a position corresponding to the position of the film outlet of the film feed cassette which has been loaded into the refrigerator. Therefore, after the film feed cassette has been loaded into the refrigerator, the long test film can be repeatedly pulled out through the film outlet of the film feed cassette and the film outlet of the refrigerator. When the long test film is to be used to analyze a plurality of liquid samples sequentially, portions of the long test film having a length equal to the minimum length necessary for a single analysis are pulled out sequentially. The long test film is forwarded just before each liquid sample is applied thereto.
Before the film feed cassette is loaded into the refrigerator, the film outlet thereof is closed in order to seal off the region inside of the film feed cassette completely. However, after the film feed cassette is loaded into the refrigerator, the film outlet of the film feed cassette is kept open. Therefore, a problem arises in that wet ambient air enters the film feed cassette through the film outlet of the refrigerator and the film outlet of the film feed cassette and causes the humidity inside the film feed cassette to increase. In order for the long test film in the refrigerator not to deteriorate, it is necessary for the region inside of the film feed cassette to be kept substantially dry (i.e. at a humidity of 0%). However, with conventional refrigerators, because wet ambient air enters the film feed cassette through its film outlet, the long test film may deteriorate within a period as short as several days. In order for wet ambient air to be prevented from entering the film feed cassette through the film outlet of the refrigerator and the film outlet of the film feed cassette, it has been suggested that a very dry air stream (having a humidity of approximately 0%) be introduced into the film feed cassette located in the refrigerator, and that such air should be made to jet from the film outlet of the film feed cassette. However, a device for generating very dry air has a high manufacturing cost.